PERFORMANCE STUDY OF BUFFER CONTROL SCHEMES AND CELL DISCARD MECHANISMS IN A SHARED BUFFER ATM SWITCH

This paper deals with overload control during congestion in a shared b uffer ATM switch via selective cell discard and buffer management. Spe cifically, we consider the question of efficiency in buffer control sc hemes in order to reduce the number of cells that have to be discarded during congestion, in the meantime provide ''fair'' access to the sha red buffer by all users. To prevent performance degradation of the sha red buffer switch under imbalance traffic conditions, a ''gated'' buff er control scheme is proposed. The concept of the ''gated'' control po licy is that we add a control gate in front of the corresponding logic al queue of each overloaded output port. Some incoming cells destined for the overloaded pens can be blocked before entering the shared buff er. It will make rooms in the shared buffer for those incoming cells d estined for the non-overloaded ports. This gated buffer control scheme can be modeled as a variation of SMXQ (sharing with a maximum queue l ength) scheme with a set of dynamically adjusted queue length threshol ds. The simulation study of the gated buffer control is applied to a s hared buffer ATM switch under various cell discard mechanisms. In most cases the proposed gated buffer control scheme can not only reduce th e overall cell loss but also satisfy the ''fair'' access requirement u nder network congestion conditions, if we adjust the dynamical queue l ength thresholds properly.